The proposed investigation is a three year study of human filariasis in the Dominican Republic. The Republic is a democratic, American-oriented, Caribbean nation which shares the island of Hispaniola with Haiti. Although virtually nothing has been published, it is now clear that this country represents a major unexplored endemic focus. Preliminary work by the investigators and local workers show that Wuchereria bancrofti is widely endemic and is a significant health problem. Geographic and socio-economic conditions are highly favorable and it may be increasing in some areas. A single case of Mansonella ozzardi has been documented and, given its wide distribution in Haiti, it is undoubtedly also widespread. Collaborative arrangements are proposed through Dr. Mercedes Garcia de Ginebra of the National University Pedro Henriquez Urena in Santo Domingo. Technician/phlebotomists are to be stationed among the various provinces of the study areas. Nocturnal 1 ml Knott blood samples and serology samples will be accompanied by a subject basic data form. Specific aims are: 1) to determine which species of human filariae are present in the study area; 2) to establish their geographic distribution; 3) by appropriate statistical analyses, to calculate specific prevalence rates for each urban area examined, to compare specific prevalences among various urban areas, and to establish statistically the major determinants of filariasis distribution in the Republic; 4) to compare the endemic areas by probit analysis of microfilaria level of positive cases; 5) to collect basic data on filarial disease, largely as reported by the patient; 6) to examine the role of antibodies in human filariasis by quantitating immunoglobulin class changes and establishing hemagglutinating titers to four antigens (three stage-specific Brugia antigens, and Brugia adult secretory antigens; 7) to examine the relationship of these serological parameters to microfilaremia, clinical signs consistent with filariasis, and differential white cell count; and 8) to continue our experimental inoculations of nude (cogenitally athymic) mice with Wuchereria bancrofti infective larvae.